I would guess that most people never think much about the barrels that their wine is aged in. This article on barrel-making is very interesting.
From the article:
Barrel-making is labor intensive. Demptos can make up to 148 barrels per day in Napa, while Seguin Moreau’s capacity is about 125 per day. Demptos employs 39 coopers and ships barrels to about 900 clients. Seguin Moreau has 22 coopers and lists nearly 1,000 clients on its roster. Both ship to wineries in other countries, including some in Europe.
In addition, both companies have facilities in Missouri, where the best American oak trees are grown.
Barrels are not inexpensive. Because each barrel is hand-made to order, French oak barrels can cost more than $850; the price varies depending on the value of the Euro on a given day.